Abnormalities of volume regulation and membrane integrity in myocardial tissue slices after early ischemic injury in the dog: effects of mannitol, polyethylene glycol, and propranolol.

The authors used an in vitro myocardial tissue slice technique to quantitate the transmural distribution of alterations in cell volume regulation and membrane integrity following early ischemic injury and to evaluate directly the effects of therapeutic interventions in a system not subjects to influences of coronary blood flow. Left circumflex coronary occlusion was produced in 57 dogs for 30 or 60 minutes. After in vitro incubation in Krebs-Ringer-phosphate-succinate medium containing trace 14C-inulin, typical values (ml H2O/g dry weight) for control nonischemic myocardial slices were 3.68 +/- 0.07 (SEM) for total tissue water, 2.67 +/- 0.07 for inulin impermeable space, and 1.01 +/- 0.04 for inulin diffusible space. Ischemic myocardial slices exhibited an impaired response to cold shock (0 C for 60 minutes) and rewarming (37 C for 60 minutes). After 60 minutes coronary occlusion, respective increases in total tissue water, inulin-impermeable space and inulin-diffusible space of ischemic slices were 25.5 +/- 2.6%, 6.2 +/- 4.9% and 84.4 +/- 12.5% for papillary muscle, 22.2 +/- 2.1%, 10.4 +/- 4.2% and 52.5 %/- 10.3% for subendocardium and 9.1 +/- 1.5%, 7.2 +/- 2.3% and 15.8 +/- 5.5% for subepicardium. Significant but usually less marked alterations occurred after 30 minutes of coronary occlusion. Propranolol treatment in vivo (2 mg/kg) and/or in vitro (0.01 mg/ml medium) produced no significant changes in tissue water or inulin spaces of ischemic slices, compared with saline controls. Incubation in hyperosmolar mediums resulted in significant reductions in total tissue water and inulin-impermeable space with little change in inulin-diffusible space of both ischemic and control slices. Fifty milliosmolar polyethylene glycol (MW 6000) produced a greater reduction in tissue water and ultrastructural evidence of cell swelling than did either 40 or 100 milliosmolar mannitol (MW 182). The major effect of hyperosmolar incubation appeared to be a selective reduction in edema of cells with structurally intact membranes. Thus, in vitro studies, with myocardial tissue slices provide evidence of widespread alterations of membrane integrity after 30--60 minutes of in vivo coronary artery occlusion. In vitro abnormalities of cell volume regulation can be partially reversed by direct osmotic effects on myocardial cells.